Constipation

Epidemiology

• Demographics: More common in elderly, females, and hospitalized/immobile pts.
• Dietary factors: Low dietary fiber, inadequate fluid intake, and physical inactivity.
• Secondary medical conditions:
  • Endocrine/Metabolic: Hypothyroidism, hypercalcemia, hypokalemia, DM.
  • Neurologic: Parkinson disease, MS, spinal cord injury, Hirschsprung disease (in neonates).
  • Structural: Colorectal cancer (CRC), rectal prolapse, anal stricture.
• Medications (highly tested):
  • Opioids (decrease peristalsis, increase water absorption).
  • Anticholinergics (e.g., diphenhydramine, TCAs, oxybutynin).
  • Calcium channel blockers (CCBs) (especially verapamil).
  • Iron supplements, aluminum antacids.

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Etiology

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Pathophysiology

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Clinical features

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Diagnostics

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Treatment

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Approach

• First-line: nonpharmacological measures (e.g., high-fiber diet, increased fluid intake, and exercise) and/or trial of bulk-forming laxatives c
• Second-line: step-wise pharmacotherapy with laxatives from other classes
  • Begin with an osmotic laxative.
  • If symptoms persist, add a short course of a stimulant laxative.

Laxatives

• Bulk-Forming
  • Psyllium, Methylcellulose
  • ↑ stool mass → stimulates peristalsis
  • Onset: 12-72h
  • SE: Bloating; needs water to prevent obstruction
• Osmotic
  • Lactulose (also for hepatic encephalopathy), Polyethylene glycol (PEG), Mg(OH)₂
  • Draw water into lumen
  • PEG: First-line for chronic constipation; safe, effective, well-tolerated
  • Onset: 0.5-3h (saline), 24-48h (lactulose)
  • SE: Dehydration, electrolyte loss; Mg²⁺ toxicity in renal failure
• Stimulant
  • Bisacodyl, Senna
  • Stimulate enteric nerves → ↑ peristalsis
  • Onset: 6-12h (oral), 15-60min (rectal)
  • SE: Cramping; chronic use → melanosis coli, cathartic colon
• Stool Softeners
  • Docusate
  • Detergent allows water penetration
  • Use: Prevent straining post-op, post-MI
• Lubricant
  • Mineral oil
  • SE: Lipid pneumonia (aspiration), ↓ fat-soluble vitamin absorption
• Secretagogues
  • Lubiprostone (ClC-2 activator), Linaclotide/Plecanatide (GC-C agonists)
  • ↑ intestinal fluid secretion
  • Use: IBS-C, chronic constipation
• Opioid Antagonists
  • Methylnaltrexone, Naloxegol
  • Block peripheral μ-receptors (don’t cross BBB)
  • Use: Opioid-induced constipation

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Fecal Impaction

Epidemiology & Risk Factors

• Epidemiology: Most common in elderly, institutionalized/nursing home residents, and pediatric populations with developmental delays.
• Risk Factors:
  • Chronic constipation.
  • Immobility/sedentary lifestyle.
  • Neurological disorders (e.g., Parkinson disease, MS, spinal cord injury, dementia).
  • Medications: Opioids, anticholinergics, iron supplements, CCBs, NSAIDs.
  • Psychiatric conditions (e.g., depression, eating disorders).

Clinical Features

• History:
  • Decreased stool frequency or inability to pass flatus/stool.
  • Paradoxical diarrhea (liquid stool bypasses the obstructing fecal mass; often misdiagnosed as infectious diarrhea). c
  • Vague lower abdominal pain, distension, tenesmus, and anorexia.
  • Urinary retention or frequency (due to extrinsic compression on bladder/urethra).
• Physical Exam:
  • Digital Rectal Exam (DRE): Palpable hard, dry, impacted stool in the rectal vault.
  • Abdomen: Distended, tympanitic, sometimes a palpable firm left lower quadrant mass. Mild tenderness, but peritonitis is absent unless perforation has occurred.

Diagnosis

• Initial: Digital Rectal Exam (DRE). Diagnostic for low/distal impaction.
• Imaging:
  • Abdominal X-ray (XR): Indicated if DRE is negative but clinical suspicion remains high (evaluates for high/proximal impaction). Shows large amounts of stool in the colon, megacolon, or dilated bowel loops with air-fluid levels.
  • Abdominal CT: Reserved for cases with suspected complications (e.g., perforation, stercoral colitis) or to rule out a mechanical mass (e.g., colorectal cancer).
• Key Labs: Generally normal. Check BMP if severe vomiting/dehydration (hypokalemia, acute kidney injury) or to rule out hypercalcemia/hypothyroidism as a cause of constipation.

Management

1. Manual Disimpaction:
   • First-line for distal/rectal impactions.
   • Perform gently using lubricated, gloved finger. May use topical lidocaine jelly to reduce discomfort.
2. Enemas & Suppositories:
   • Indicated after manual disimpaction or if stool is out of reach of manual extraction.
   • Use mineral oil enemas (to lubricate) or warm water/phosphate enemas (to stimulate motility).
   • Note: Avoid phosphate enemas in elderly or renal insufficiency due to risk of hyperphosphatemia.
3. Oral Laxatives (Maintenance & Proximal Impaction):
   • Polyethylene glycol (PEG) is highly effective once the distal rectum is cleared.
   • Contraindication: Do NOT give oral laxatives (especially osmotic/stimulant) if complete distal obstruction is present, as it can cause severe abdominal cramping, vomiting, or perforation.
4. Prevention:
   • Increase dietary fiber, fluid intake, and physical activity.
   • Minimize constipating medications; use prophylactic bowel regimens if opioids are mandatory (e.g., senna + docusate, methylnaltrexone).